Changes In Solar Insolation Research Articles

On the forcing of seasonal changes in surface pressure over Antarctica

A 10‐year record (1985–1994) of output statistics from the European Centre for Medium‐Range Weather Forecasts (ECMWF) model shows that profound seasonal changes in surface pressure take place over the Antarctic continent. The most pronounced changes occur during the periods straddling the brief Antarctic summer, from September to December and again from January to April. Surface pressures atop the high Antarctic plateau often display changes in excess of 20 hPa during these periods. Temperatures in the lower troposphere also exhibit marked changes during these transitional periods; surface temperature changes during these 3‐month periods reach a maximum near 40 K over the high interior of Antarctica. Hydrostatic considerations suggest that the thermal adjustment in the lowest levels of the atmosphere alters the vertical distribution of pressure with height and hence is consistent with the dramatic seasonal surface pressure changes over the elevated Antarctic ice sheets. A strong interplay exists between the thermal forcing and the katabatic wind circulation over the continent. The large seasonal changes in solar insolation reaching the Antarctic ice surface modulate the intensity of the katabatic wind regime and thus the resulting mean meridional circulation between the continent and the subpolar latitudes. It is proposed that the diabatic adjustment in the lower levels of the atmosphere over Antarctica disrupts the mean meridional circulation creating a seasonal mass imbalance and hence surface pressure changes. It is through the meridional transports that the mass and wind fields reach a quasi‐equilibrium adjusted state. The seasonal mass movement over Antarctica requires large‐scale mass compensation over much of the southern hemisphere and shows that the diabatic influences at the Antarctic surface have far‐field impacts.

Orbital forcing of deep-sea benthic species diversity

Explanations for the temporal and spatial patterns of species biodiversity focus on stability–time1–3, disturbance–mosaic (biogenie microhabitat heterogeneity)4,5 and competition–predation (biotic interactions)6,7 hypotheses. The stability–time hypothesis holds that high species diversity in the deep sea and in the tropics reflects long-term climatic stability3. But the influence of climate change on deep-sea diversity has not been studied and recent evidence suggests that deep-sea environments undergo changes in climatically driven temperature8 and flux of nutrients9 and organic-carbon10 during glacial–interglacial cycles. Here we show that Pliocene (2.85–2.40 Myr) deep-sea North Atlantic benthic ostracod (Crustacea) species diversity is related to solar insolation changes caused by 41,000-yr cycles of Earth's obliquity (tilt). Temporal changes in diversity, as measured by the Shannon–Weiner index, H(S), correlate with independent climate indicators of benthic foraminiferal oxygen-isotope ratios (mainly ice volume11–13) and ostracod Mg:Ca ratios (bottom-water temperature8). During glacial periods, H(S) = 0.2–0.6, whereas during interglacials, H(S) = 1.2–1.6, which is three to four times as high. The control of deep-sea benthic diversity by cyclic climate change at timescales of 103–104 yr does not support the stability–time hypothesis because it shows that the deep sea is a temporally dynamic environment. Diversity oscillations reflect large-scale response of the benthic community to climatically driven changes in either thermohaline circulation, bottom temperature (or temperature-related factors) and food, and a coupling of benthic diversity to surface productivity.

Investigating the sensitivity of the Atmospheric General Circulation Model ECHAM 3 to paleoclimatic boundary conditions

We present atmospheric simulations of three different time slices of the late Quaternary using the ECHAM 3 general circulation model in T42 resolution. In this work we describe the results of model runs for the time slices 6000 years BP (last climate optimum), 21 000 BP (last glacial maximum) and 115 000 years BP (glacial inception). Although the solar insolation is known for all time slices, a complete data set of the other boundary conditions which are necessary for running the atmospheric model exists only for the last glacial maximum in the form of the CLIMAP reconstruction. For the other two time slices, which are interglacial states like the modern climate, sea surface temperatures, land albedo and ice sheet topography are kept at modern values and only the solar insolation is changed appropriately. The response of the model to solar insolation changes is quite reasonable. The modelled anomalies are small and roughly opposite in sign for 6000 BP and 115 000 BP, respectively. In the case of last glacial maximum, the glacial ice sheet topography and ice albedo produce a much larger climate anomaly in the model. However, to enable a real test of model performance under glacial boundary conditions, the CLIMAP sea surface temperatures, which are now known to be partly inaccurate, should be replaced by an updated “state-of-the-art” reconstruction.

Tropospheric formaldehyde concentration at the Mauna Loa Observatory during the Mauna Loa Observatory Photochemistry Experiment 2

The concentration of formaldehyde at Mauna Loa Observatory, Hawaii, was determined during four Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) measurement intensives between September 1991 and August 1992. The observed diurnal variations, 200–900 parts per trillion by volume (pptv) during daytime and 60–200 pptv during nighttime, resulted mainly from the local air circulation pattern whereby island modified marine boundary layer air prevailed during the day and free tropospheric air dominated during the night. A seasonal variation was also observed; the median/mean values of all data points are: 149/196, 129/149, 143/178, and 181/211 pptv for autumn, winter, spring, and summer intensives, respectively. During nighttime downslope flow periods which brought in free tropospheric air to the measurement site, the formaldehyde concentrations (median/mean) were 122/123, 110/112, 120/125, and 140/137 pptv for autumn, winter, spring, and summer, respectively. This seasonal dependence may be attributable to changes in solar insolation and NO concentrations. A simple box model calculation constrained by the experimentally determined concentrations of CH3OOH yielded a formaldehyde concentration (without/with heterogeneous removal) for free tropospheric air, at 7°C, of 155/140, 125/115, 210/195, and 220/205 pptv for autumn, winter, spring and summer, respectively. The calculated values are in good agreement with the measured concentrations for winter (within 27/15%, without/with heterogeneous removal) and fall (within 14/5%), but are significantly higher for spring (75/63%) and summer (57/46%).

Magnetostratigraphic, biostratigraphic, and stable isotope stratigraphy of an Upper Miocene drill core from the Salé Briqueterie (northwestern Morocco): A high‐resolution chronology for the Messinian stage

We report a high‐resolution stable isotope, carbonate, magnetostratigraphic, and biostratigraphic record from a 175‐m drill core from the Salé Briqueterie, which is part of the Bou Regreg section in northwestern Morocco. The Salé drill core spans the interval from paleomagnetic Chron C4n partim to C3r (earliest Gilbert), which represents the time leading up to and including the isolation and desiccation of the Mediterranean (i.e., the Messinian salinity crisis). During Chrons C3An and C3Ar (6.935 to 5.894 Ma) the isotope and carbonate signals display quasi‐periodic variations with estimated periods of 40 and 100 kyr, respectively. We interpret the 40‐kyr δ18O variations as reflecting changes in global ice volume caused by obliquity‐induced changes (41 kyr) in solar insolation in polar regions. The 100‐kyr carbonate variations probably represent long‐term modulation of the amplitude of the precessional cycle (∼21 kyr), which is not resolved by our sampling frequency. The cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of Shackleton et al. (1994a) from stage TG24 in Chron C3r (earliest Gilbert) to stage C3Ar.δ18O.18 at the base of Chron C3Ar (6.935 Ma). A major change in paleoceanographic conditions is recorded across the Tortonian/Messinian boundary, which we correlate to Chron C3Bn at 7.04 Ma. Benthic foraminiferal δ18O values increased by an average of 0.4‰ in two steps at 7.17 Ma and 6.8 Ma and δ13C values decreased by 0.7–0.8‰ between 7.1 and 6.8 Ma, representing the late Miocene carbon shift. The first step in δ18O values coincides with an inferred reversal in deep water circulation through the Rifian Corridor, and the second correlates with the base of the Tripoli Formation and onset of “crisis conditions” in the Mediterranean. We suggest that the increase in δ18O values represents, at least in part, an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the Mediterranean. Average δ18O values remained high throughout most of Chrons C3Ar and C3An, reaching maximum δ18O values during isotope stages TG20 and 22 in Chron C3r (earliest Gilbert). The glacio‐eustatic falls associated with these events may have resulted in the complete isolation of the Mediterranean from the world ocean (Shackleton et al., 1994a). Following stage TG12 in the Salé record, there exists a trend toward progressively lower δ18O values that may represent a series of marine transgressions that eventually reflooded the Mediterranean and ended the Salinity Crisis.

Changes in stratospheric aerosols and solar insolation due to Mt. Pinatubo eruption as observed over the western Pacific

Effects of the Mt. Pinatubo eruption on the stratospheric aerosols and the solar insolation over the Western Pacific were estimated by sunphotometer and pyranometer on board ships. The sunphotometer measurements showed that the columnar aerosol optical thickness increased by 0.3 at 500 nm over the latitude from 30°N to 30°S, while that without the influence of volcanic eruptions is less than 0.1. The aerosol optical thickness became minimum in the summer of 1992, and increased again after the summer. The shipboard pyranometer measurements showed that solar insolation decreased after the eruption by 1.4∼4.1% compared with that before the eruption. This value is larger than that calculated with radiative transfer code, based on the aerosol model estimated from the sunphotometry.

Initial results of U.S.‐Soviet paleoclimate study of Lake Baikal

Lake Baikal, a Miocene‐age rift lake in southeastern Siberia, is an especially promising site for paleoclimate studies. Its high‐latitude location (52°–56°N) makes it particularly sensitive to changes in solar insolation due to long‐period variations in the Earth's orbital parameters. These variations are widely believed to be the main forcing functions of climate change in the Quaternary [Hays et al., 1976; Imbrie et al., 1984. The extreme continentality of the climate in southeastern Siberia makes Baikal an ideal location to study temporal changes in seasonality. Baikal is also one of the few high‐latitude lakes that has not been glaciated during the last 1–2 million years [Grosswald, 1980], although a record of glaciation in its drainage basin is preserved in the lake sediments. Finally, Lake Baikal is the largest (23,000 km3), the deepest (1640 m), and one of the oldest extant lake systems in the world. The sedimentary section in the Baikal depression is more than 7 km thick and probably spans more than 15 million years [Hutchinson et al., 1992]. Accordingly, Lake Baikal sediments represent one of the longest and most complete continental climate records available anywhere in the world.

Growth Rate Responses of Lotic Periphytic Diatoms to Experimental Phosphorus Enrichment: The Influence of Temperature and Light

Phosphate enrichment experiments were conducted year-round at the experimental troughs research apparatus (EXTRA) on the South Thompson River in British Columbia to determine the relationship between external concentration of orthophosphate and the growth rates of lotic periphytic diatom communities. Growth rate saturation always occurred at a phosphate concentration of approximately 0.3–0.6 μg P∙L−1. The maximum growth rate (μmax-P) with phosphorus enrichment varied seasonally with temperature. The relative specific growth rates (μ:μmax-P) as a function of external phosphate were constant. Seasonal changes in solar insolation (PAR) had no effect on the autotrophic community growth rates in unamended river water. Temperature exerted the most dominant influence on phosphorus-replete growth rates.

Potential productivity and surface circulation in the northern Indian Ocean during the last glacial-to-interglacial transition: Application of a new paleoceanographic model

A new paleoceanographic model is presented which approximates concentrations of total PO 4 for the upper water column for the recent geologic past using the isotopes of carbon and oxygen from the tests of monospecific assemblages of planktic foraminifera. These calculated concentrations of total PO 4 are, in turn, used to estimate relative changes in potential productivity as well as changes in the position and intensity of surface currents for the recent geologic past. This new model is based uponthe statistical constancy of the Redfield ΔO 2: ΔPO 4 ratio in the modern oceans and has been shown to be an accurate and reliable predictor of total PO 4. The down core application of this model, thus far limited to five core sites in the northern Indian Ocean, has yielded results which are consistent with a number of other studies in characterizing the last glacial maximum in the northern Indian Ocean, as a time of reduced potential productivity and weak surface currents. In contrast, by 9 ky B.P., the potential productivity and the surface circulation had increased dramatically in the northern Indian Ocean. Conditions in the Holocene appear to be very similar to conditions which were in existence during the last glacial maximum. The observed general trends in surface circulation and potential productivity during the last 18,000 years in the northern Indian Ocean suggest a Milankovitch-type (astronomically induced changes in solar insolation) orbital forcing.

Modelling the global climate response to orbital forcing and atmospheric carbon dioxide changes

At least part of the record of climate change during the past million years may be attributed to forcing by changes in the geometry of the Earth's orbital system. Several attempts have been made to model the record of climate change (usually represented by the record of global ice volumes as recorded in marine sediments) using astronomical forcing1,2. These models have, in general, concentrated on the direct response of the ice sheets to changes in solar insolation resulting from orbital variations. So far no fully successful simulation of the climate record has been made. We investigate here the operation of a model which is forced simultaneously by changes in the distribution of solar insolation caused by orbital variations and by changes in the atmospheric carbon dioxide (CO2) concentration which are themselves forced by orbital parameters. The model results show the potential importance of other components in the climate system and their associated response to changing orbital parameters.

Solar Irradiance Model for Solar Electric Panels and Solar Thermal Collectors in Lithuania

Presented the model based on the clear sky standard, which allows calculation of solar insolation values at each location in Lithuania. Model is associated with geographical coordinates of Lithuania and local time of every day of the year. It is made for modeling electronic systems for management of solar panels and solar thermal collectors. Model was tested by calculating solar insolation at 313 369 locations of Lithuania. It is shown that the lowest insolation in territory of Lithuania on noon of June 21 is 375 m2 and the highest is – 439 W/m2. Deviation of solar insolation values from average is ±8%. In addition, it is shown that the changes in solar insolation are caused by zenith or altitude angle variations. Model is suitable for calculation of optimal angles of solar panels and solar thermal collectors in any location of Lithuania. Ill. 4, bibl. 8 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.108.2.132